1. Field of the Invention
The present invention relates to an encoding device in mobile communication systems, and more particularly, to a quasi-orthogonal code mask generating device.
2. Description of the Related Art
In CDMA (Code Division Multiple Access) communication systems, orthogonal modulation using orthogonal codes provides channelization among code channels as a way of increasing channel capacity. IS-95/IS-95A applies the orthogonal channelization on a forward link, and a reverse link can be applied through time alignment.
Channels on the forward link in IS-95/IS-95A are distinguished by different orthogonal codes as shown in FIG. 1. Referring to FIG. 1, xe2x80x9cWxe2x80x9d indicates an orthogonal code and each code channel is identified by a preassigned orthogonal code. The forward link uses a convolutional code with a code rate R=xc2xd, BPSK (Binary Phase Shift Keying) modulation, and a bandwidth of 1.2288 MHz. Therefore, orthogonal codes can provide channelization among 64 forward channels (=1.2288 MHz/9.6+2).
Once a modulation scheme and a minimum data rate have been determined, the number of available orthogonal codes can be obtained. In the future CDMA communication systems may increase channel capacity by increasing the number of channels, which includes a traffic channel, a pilot channel, and a control channel resulting in improved performance.
However, the increase in the number of channels causes a shortage in the number of available orthogonal codes, thereby limiting channel capacity. This disadvantage can be overcome by using quasi-orthogonal codes, which incur minimum interference with orthogonal codes, and a variable data rate.
The generation of quasi-orthogonal codes is disclosed in Korea Application Patent No. 97-47257. In order to generate a quasi-orthogonal code, quasi-orthogonal code sequence mask values are stored in a memory and retrieved for use as needed. If a mask value occupies 64 bits, a 64-bit memory is required. Therefore, the conventional quasi-orthogonal code mask generation scheme has a disadvantage of requiring increased hardware complexity.
Therefore, an object of the present invention is to provide a device for generating quasi-orthogonal code mask values with minimum interference with orthogonal codes in a mobile communication system which uses orthogonal codes.
Another object of the present invention is to provide a device for generating quasi-orthogonal code mask values using a Bent function in a mobile communication system which uses orthogonal codes.
To achieve the above objects, a device for generating a quasi-orthogonal code mask in a communication system is provided. In the device, a counter generates first to eighth counter signals x1-x8 representing Bent functions, and a logic operator receives the first to eighth counter signals x1-x8 and performs an operation of x1*x2 +x1*x3+x1*x4+x1*x5+x1*x7+x1*x8+x2*x6+x2*x7+x3*x4+x3*x5+x3*x6+x4*x5+x4*x6+x4*x7+x4*x8+x5*x7+x7*x8+x1+x2+x5+x7 to generate a mask signal.